Fluorine-containing compounds are developed and used in a wide application field of advanced materials, due to properties owned by fluorine, such as water-repellent property, oil-repellent property, low water absorption, heat resistance, weather resistance, corrosion resistance, transparency, photosensitivity, low refractive index, low dielectricity, etc. Particularly recently, there have been active researches on resist materials of fluorine-containing compounds as novel materials having a high transparency to short wavelength ultraviolet rays such as F2 laser and ArF excimer laser. A common molecular design in these application fields is based on the achievement of properties such as transparency at each wavelength used by introducing fluorine, photosensitivity utilizing acid properties of fluoroalcohol such as 1,1,1,3,3,3-hexafluoroisopropyl-2-hydroxy group (it may be referred to as hexafluoroisopropyl hydroxyl group), and adhesive property to the substrate.
On the other hand, together with the trend toward micro-scale device structure, there has been a demand for micro-scale resist pattern in lithography step, and the improvement of an exposure apparatus has been studied.
For example, stepper (reduced projection type exposure machine) has greatly been improved in resolution too by the improvement of performance of reduced projection lens and the improvement of optical system design. The performance of a lens used in stepper is expressed by NA (numerical aperture), and a value around 0.9 is said to be physical limit in the air. At present, it has already been achieved. Therefore, there has been an attempt to raise NA to 1.0 or greater by filling the space between lens and wafer with a medium having a refractive index higher than that of air. In particular, an exposure technique by an immersion procedure using pure water (hereinafter it may be referred to as simply water) as the medium has attracted attention (Non-patent Publication 1).
In immersion lithography, a resist film is brought into contact with the medium (e.g., water). Therefore, various problems have been pointed out. In particular, the pattern shape change caused by that an acid generated in the film by exposure or an amine compound added as quencher is dissolved in water, the pattern collapse caused by swelling, etc. becomes problems. Then, there has been a report that it is effective to form a top coating film on the resist to have a separation of the resist film and water (Non-patent Publication 2).
Therefore, the top coating composition is required to have properties such as a good developing solution solubility, resistance against pure water, separation of the resist film and water, no corrosion on the resist film of the underlayer, etc. As a top coating composition satisfying such requirement, there has been developed a composition containing a fluorine-containing polymer having a repeating unit containing a unit containing at least two hexafluoroisopropyl hydroxy groups, and there has been a report that it is superior particularly in developing solution solubility (Patent Publication 1).
Fluorine-containing resist composition is effective for improving water repellency. Hitherto, various fluorine-containing polymers for fluorine-containing resists have been developed. The present applicant discloses a difluoroacetic acid ester having a polymerizable double bond-containing group and an acid-labile protecting group (Patent Publication 2) and a difluoroacetic acid having a polymerizable double bond-containing group (Patent Publication 3).